Photonic crystals are crystals having a regular structure of which the lattice distance is tens of nanometers to several micrometers, and are capable of regulating the optical properties in a range of ultraviolet rays, visible rays and infrared rays. Such photonic crystals exist in the natural world, for example opals, butterflies, and shells etc. each emitting beautiful light, and have been developed artificially by observing the structure of the natural crystals and then manufactured.
Typical methods of manufacturing such photonic crystals include the top-down method, such as photolithography and ion beam etching used in a conventional semiconductor process, and a bottom-up method used regularly to arrange nanoparticles with a uniform dimension.
The method of manufacturing photonic crystals through the conventional photolithography and ion beam etching has the advantage of making sophisticated regular structures, but has the disadvantages of very high incidental expenses and a long time being required to prepare large scale photonic crystals. On the other hand, the method of manufacturing photonic crystals through self-assembly of nanoparticles (Korean patent laid open 2003-0083913) has the advantages that no incidental equipment is required and it is possible to prepare large scale photonic crystals in less time, however it is also difficult to prepare large scale photonic crystals with no defects. Thus, in the field of preparing photonic crystals, a technology capable of building large scale photonic crystals with no defects in less time through the self-assembly of nanoparticles is an essential subject for commercial usage.
In particular, the preparation of photonic crystals using high molecular colloidal nanoparticles has been widely studied recently, and there are various methods such as a deposition method by gravity [H. Miguez et al., Adv. Mater. 10,480(1998)], a vertical deposition method [P. Jiang et al., Chem. Mater. 11,2132 (1999)], a vertical deposition method through a temperature distribution [Y. A. Vlasov et al., Nature(London) 414,289(2001), J. D. Joannopoulos, Nature(London) 414,257(2001)], and an electrophoresis method [A. L. Rogach et al., Chem Mater. 12,2721 (2000)] etc.
The deposition method by gravity uses a phenomenon that, when motionlessly laying a solution in which a high molecular silica colloid is dispersed for a long time, particles are deposited onto the bottom by gravity and then are self-assembled. However, this method has the disadvantages that processing time is very long and the photonic crystals have defects. In addition, other methods are capable of preparing large scale photonic crystals in less time but also have a problem in that the photonic crystals have defects.
Further, in the case of preparing 2 or 3 dimensional photonic crystals using the polymer colloidal particles, spherical colloidal particles are generally self-assembled in the structure of a face centered cubic (FCC). In this case, the particles in a colloidal solution self-assemble onto a substrate as the solution is vaporized, the colloidal particles having liquidity in the case that the volume ratio thereof is up to 54%, but are crystalloid with no liquidity in the case that the ratio is more than that. Thereafter, the solution is vaporized until the volume ratio of the colloidal particles is 74%, the volume of the self-assembled colloidal particles in the crystalloid is thus contracted [Cheng et al., Nature (London) 410,893 (1999)]. In such a process of drying the solution, the colloidal particles are subjected to a nonuniform volume contraction thereby creating defects.
To solve the problem of defects resulting from such a volume contraction, a method using a liquid metal with liquidity as a substrate component may be used, but there is a problem in that it is difficult to apply commercially [Griesebock et al., Chem mater., 14,4023 (2002)].